Due to its satisfactory handleability combined with its excellent properties such as mechanical and electrical properties as well as the resistance to heat and weather, unsaturated polyester resins are widely used as casting materials, coating materials, putty, adhesives, various types of linings, FRP etc. However, the unsaturated polyester resin products are hard and fragile, in other words, of less elongation and impact strength and, in most cases, incur problems such as breakage or cracking caused by impact in the course of production or transportation. Consequently, such products are considered unsuitable for use in applications where they are subjected to repeated impact and their use is indeed restricted to a considerable extent. Especially in the case of FRP, the demand for which is expanding as a substitute for metal, it is desired to improve the strength and toughness thereof, which properties are considered of vital importance. Even in the case of an epoxy acrylate resin, introduced with a view to eliminating and improving the brittleness and the resistance to chemicals of the unsaturated polyester resin, there is still much to be desired with respect to toughness.
To impart toughness to a resin, it has generally been proposed to plasticize the resin or add a rubber component thereto. In the former method, however, insufficient toughness is obtained, yet there is a decrease in heat resistance and mechanical strength. The latter method gives rise to an improvement in the toughness of a resin composition containing chopped strand glass and inorganic fillers such as BMC and SMC; however, its practical use is restricted to some extent since the resin composition is unstable; a product obtained therefrom by hardening suffers color shading; and the like. In fact, a rubber component has not been found, which has a toughness-imparting effect on FRP combined with casting or reinforcing materials.
As a result of extensive studies carried out for the purpose of obviating the disadvantages of the prior art unsaturated polyester and/or epoxy acrylate resins, it has been found that an unsaturated acrylic urethane has a toughness-imparting effect.